1. Field of the Invention
The invention relates to a mechanism for ink monitoring by acquiring the level-dependent change in resistance between two electrodes in ink printer devices.
2. Description of the Prior Art
Ink printer devices require an ink reservoir from which the ink is supplied to the individual write nozzles directly and bubble-free. Current ink reservoirs are provided as replaceable parts, whereby the flow connection between the ink reservoir and the ink printer device occurs through a hollow needle which penetrates a sealing element when the ink reservoir is put in place. Monitoring the filling level of the ink reservoir is accorded great significance. One of the reasons for this is that air can enter into the ink supply system via a completely empty reservoir, this air leading to a considerable operating malfunction.
In a known mechanism for monitoring the supply of writing fluid in an ink reservoir, two electrodes are employed via which a change in resistance dependent on the level of the fluid in the reservoir is acquired and is evaluated in a circuit arrangement (U.S. Pat. No. 4,202,267). In accord with this prior art, the one electrode is formed by the hollow needle which produces a connection between the ink supply system and the ink reservoir. A rivet secured in the floor of the ink reservoir serves as the second electrode. The second electrode can also be formed in that at least the floor part of the ink reservoir is coated with an electrically conductive layer. When the ink volume in the ink reservoir is diminished, the electrical resistance between the electrodes increases, this leading to the initiation of a warning apparatus in the following circuit arrangement and leading to the output of a warning signal.
In the known apparatus, the second electrode is conducted parallel to the hollow needle through the sealing element. This frequently leads to problems, since the material stressing of the extremely small sealing element becomes so great as a result thereof that an absolutely ink-tight closure is no longer guaranteed. Particularly when the ink reservoir is not placed on the hollow needle from above, but, on the contrary, is put in place in a horizontal direction, problems derive since the second electrode must be conducted through the sealing element in the immediate proximity of the hollow handle.